carbon steel vs stainless steel pipe

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When selecting between carbon steel and stainless steel pipes, it's essential to consider factors like corrosion resistance, cost, and specific application requirements. Carbon steel pipes are known for their strength and affordability, but they can be susceptible to corrosion in untreated environments. On the other hand, stainless steel pipes offer superior corrosion resistance and longevity, making them ideal for applications involving corrosive substances.

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carbon steel vs stainless steel pipe

kepharda

(Mechanical)

(OP)

15 Dec 06 11:47

I am piping cooling tower water supply (600 gallons per minute) header. Supply and return will be about 100 ft. long. I can get sch 10s Stainless Steel for about $59 per foot. Customer initially wanted me to investigate CPVC, but it would require a larger pipe to keep velocities down and sch 80 so it was pretty expensive for PVC at about $55 per foot. The other option would be carbon steel, but I am concerned about corrosion, sure the water will be treated, but it is an open cooling tower, so in my limited experience (4 years) there is always corrosion. My question is this is there a carbon steel pipe that would be economical to install instead of the Stainless Steel that wouldn't corrode quickly? Also, this pipe will be welded, please do not suggest threading. Thanks for any help.

RE: carbon steel vs stainless steel pipe

katmar

(Chemical)

15 Dec 06 11:59

I agree with you that threaded pipes should be avoided at these sizes. Here in South Africa, it would be most unusual to use Stainless Steel for a cooling water duty. I have seen carbon steel cooling water pipes that have been in use for 40 years. One thing I have noticed over the past few years is that installation labor is becoming a progressively higher percentage of the overall cost, so using a light gauge pipe (e.g., 10S) might save some installation costs. Also, look at the supports you will need - you may not get the same span length with Sch10S as you would with Sch40 CS.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: carbon steel vs stainless steel pipe

bimr

(Civil/Environmental)

15 Dec 06 12:01

The water will be treated such that you will get satisfactory service from carbon steel. Carbon steel is commonly used in this application. If you are concerned about the corrosion, you can use a heavier pipe thickness or go with the stainless. Stainless would be considered a step up above the standard pipe material. You are correct in that it is not a good idea to consider CPVC for this application. CPVC would be considered as a step down in quality.

RE: carbon steel vs stainless steel pipe

kepharda

(Mechanical)

(OP)

15 Dec 06 12:12

The one thing I failed to mention is that the system will connect to various pieces of equipment some having pipe connections as small as 1/2 in (12.7 mm) so while I am not worried about the pipe completely corroding through the wall, my concern more is the accumulated pipe rot that might plug lines and equipment cooling jackets. Does anyone have some similar experience that could tell me if this will be a big issue or not? Thanks.

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RE: carbon steel vs stainless steel pipe

rconner

(Civil/Environmental)

15 Dec 06 14:49

I know also cement mortar lined ductile iron piping has been used in many different cooling water applications in sizes up to at least 60" in the USA. In the size range you are perhaps talking about (I'm guessing ~10 inch diameter?), perhaps this pipe material might also be reasonably competitive with the other types of pipe you mention, and the standard cement mortar lining might well be helpful in the minimization of pipe "rot" you fear (also the maintenance of long-term flow properties). Restrained joints (and even field-adaptable restrained joints) as well as ready tapping/connection devices/procedures for all sizes of connections are readily available for such piping in such size ranges that do not require field welding.

RE: carbon steel vs stainless steel pipe

civilperson

(Structural)

15 Dec 06 17:18

After designing your carbon steel pipe, add 1/8" additional wall thickness corrosion allowance.

RE: carbon steel vs stainless steel pipe

stanier

(Mechanical)

18 Dec 06 19:18

Filed fitting and welding stainless is a lot more efficient. Having to wait weeks for DICL make spools is a risk and costly in time. Spiral wound stainless steel is commonly used in water treatment works in Australia. Flanged ductile iron is no longer the preferred material of choice due to costs of material plus labour.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au

RE: carbon steel vs stainless steel pipe

rconner

(Civil/Environmental)

19 Dec 06 10:44

While certainly not denying the utility of steel, or for that matter stainless steel, pipes in e.g. some plant piping applications ductile iron pipes have a quite good record of application and durability in particularly large water, wastewater plants, pump stations, and other applications in the USA.

RE: carbon steel vs stainless steel pipe

kepharda

(Mechanical)

(OP)

19 Dec 06 15:50

Thanks for all the responses; I got quotes from the local suppliers for carbon steel, stainless steel, and ductile iron. For the project, my recommendation to the customer was stainless because of the relatively short length of the pipe run (~200 ft) and small difference in cost (about $23/ft). I haven't received a reply back yet so we will see.

Thanks again,

-dave

RE: carbon steel vs stainless steel pipe

PersianEng

(Mechanical)

19 Dec 06 16:55

You could also get a quote for PVC coated carbon steel pipe. Probably it will be cheap enough and make the client happy that you think of cutting all possible expenses.

RE: carbon steel vs stainless steel pipe

rconner

(Civil/Environmental)

19 Dec 06 17:03

There is sometimes a perception that "stainless" is a more bulletproof material than other pipes when it comes to corrosion. However, no piping material is completely bulletproof with regards to aesthetics or actual performance failures, depending on specifics of the construction, application, operation, and exposure. In this regard I had noticed that the General Electric company presented a paper at a relatively recent NACE conference in Houston that is now available at http://www.nace-houston.org/CAC%20Papers/Mel%20Esmacher,%20Behavior%20of%-Series%20Stainless%20Steels.pdf If you have not already done so, you may wish to read such information to at least familiarize yourself with these issues, as these piping systems can be more complex in construction and application than the perception of just weld them up and go.

RE: carbon steel vs stainless steel pipe

kepharda

(Mechanical)

(OP)

19 Dec 06 18:35

Thank for the tip, I read the presentation, but most of those problems will not be an issue with my project. Temps will be below 100 F The pipe run isn't to be buried. The minimum velocities that they recommended is a good tip, fortunately I had already designed for about 7 ft/s. I have experience with designing piping systems, just not cooling water, so I do understand the complexities of installing welded piping.

RE: carbon steel vs stainless steel pipe

fergusx

(Mechanical)

11 Jan 07 04:51

If you are considering use of carbon steel be aware of risks of accelerated corrosion at least 5 times normal for sealed systems. In reality this can be a lot higher if water treatment regime is not adhered to correctly. I am currently looking at an open chilled water system in Ireland with pipe wall failures after only seven years. Carbon steel is suitable as long as the correct water treatment is in place, the correct jointing methods are used (flanging) and the correct pipe schedule is selected that is schedule 80 for 65mm dia and below.

RE: carbon steel vs stainless steel pipe

kepharda

(Mechanical)

(OP)

25 Jan 07 11:10

Thanks fergusx, I ended up at almost exactly the spec you proposed. I have also made it clear to the owner the need for water treatment once the system is assembled and even put him in contact with a couple of treatment companies. Hopefully this will be enough.

-dave

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